Sprockets, discs, wheels and similar members, that are mounted on a vertical shaft and are driven by means of a key that is disposed in the keyway defined jointly by a keyway in the shaft and a keyway in the member itself, have a tendency to slide downwardly on the key and move out of engagement therewith.
It is an object of the present invention to provide apparatus for preventing a driven member on a vertical shaft from inadvertently moving downwardly out of engagement with the shaft.